The vast majority of the plants are in one way or another hermaphrodite. Either each flower carries both male and female sex organs, or plant has both male and female flowers. Only 4 percent of the plants from these two options differ. Only for this small group of plants, there is a distinction between male and female plants, a system known as dioecy.
Botanists distinguish between perfect and imperfect flowers. Perfect flowers have both male and female sex organs. Imperfect flowers lack one or the other structure. Flowers that have only stamens as staminate or male flowers with stamps are pistillate or female. Plants with imperfect flowers can be either monoecious or dioecious. In monoecious species, staminate and female flowers occur on the same plant. When staminate and female flowers occur on different plants, the species is dioecious. Examples of dioecious plants include willow, papaya, kiwi and asparagus.
Dioecious species produce seeds through cross-pollination – pollen from a male plant fertilizes the eggs of a female plant. This means that dioecious species divide the labor of reproduction: Female plants bear seeds, while male plants produce pollen. In this sense, it is not generally possible for a male plant to produce seed of any kind, male or female. In exceptional circumstances, however, can be female and male plants of certain species bear seeds.
In dioecious species bear only female plants seeds. The plants that could grow from these seeds male or female. In some species, the sex of a seed is determined genetically. For example, in white campion (Silene latifolia) female seeds hold AA combination of genes, while the male sperm have Aa combination. In other dioecious species sex varies with environmental conditions. For example, female spinach and jack-in-the-pulpit plants to male change in the drought, and men can be female, under favorable conditions. These changes are strategic: pollen production puts less stress on the plant will produce a seed does.
A disadvantage of dioecy is the condition that exists both male and female plants to produce seeds. Some dioecious species to meet this challenge by providing a secondary strategy of asexual seed production called apomixis. The pandan dioecious plant, for example, usually produces seeds sexually. If a female flower reaches a certain age without receiving pollination, but it brings seeds apomictically. The resulting seeds are genetic clones of the mother plant. Apomixis also occurs in some non-dioecious plants such as marigold (Taraxacum officinale) and common bramble (Rubus fruticosis).